Several studies have reported improved IVF by shortening the time of sperm-oocyte coincubation from 16-18 hours to 1-4 hours. The objective of this study was to examine the advantages and disadvantages of a shortened sperm-oocyte coincubation time in order to assess the effects of this insemination method for clinical IVF practice. Two insemination methods, the shortened method (4 hours) and the standard method (16-18 hours) of coincubation of sperm-oocytes for two groups of patients based on the quality of sperm were compared. Group I, was composed of couples without male factor; Group II, involved couples with mild male factor. Fertilization, good quality embryos, clinical pregnancy, and implantation rates were compared by two different insemination methods. In Group I, fertilization, clinical pregnancy, and implantation rates were not different between the two insemination methods. However, the polyspermy rate was significantly higher (P < 0.05) in the shortened (7.3%) than in the standard (4.1%) insemination method. In Group II, the fertilization rate was significantly lower (P < 0.05) using the shortened insemination method (62.6%) compared to the standard insemination method (68.7%). When fertilization failed with the shortened insemination method, the clinical pregnancy and implantation rates were 34.7% and 24.1%, respectively, from the rescue intracytoplasmic sperm injection (ICSI). The live birth rate from the rescue ICSI was 32.0% with normal infants. The duration of sperm-oocyte coincubation does not affect fertilization, embryo quality, clinical pregnancy, and implantation rates. However, fertilization rates will decrease with the shortened insemination method when the sperm parameters are poor. From the results of the present study we suggest that the combination of the shortened sperm-oocyte coincubation and rescue ICSI method may be an efficient method for IVF treatment in order to prevent fertilization failure when sperm parameters were poor as mild male factor.